Pressure measurement devices, methods, and systems

ABSTRACT

A pressure measurement system for use in blood circuits comprised of a pressure sensing pod and a force measurement device. The pressure sensing pod can include a flexible, moveable, fluid-impermeable diaphragm and can be formed via either a one-shot or a two-shot molding process. A mechanical engagement member of the force measurement device engages with a mechanical engagement feature of the diaphragm, and the engagement member is operative to move in concert with movement of the engagement feature of the diaphragm based on pressure variations with the pressure sensing pod. The force measurement device generates and outputs to a processor a signal based on detected force associated with movement of the engagement member.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national stage entry of InternationalApplication No. PCT/US12/40298 filed May 31, 2012, which claims thebenefit of U.S. Provisional Application No. 61/491,869 filed May 31,2011 and U.S. Provisional Application No. 61/544,266 filed Oct. 6, 2011,all of which are hereby incorporated by reference herein in theirentireties.

FIELD

The disclosed subject matter relates generally to pressure measurementdevices, methods, and systems and more particularly to pressuremonitoring for medical applications.

BACKGROUND

FIG. 1 shows a pressure measurement pod 10 according to the prior art.In the pod 10, air chamber 45 is in communication with an air port 12and air line 40 that can be connected to a pressure transducer (notshown). Fluid flows through a fluid chamber 60 between an inlet line 35connected to an inlet port 70 and out of the fluid chamber 60 through anoutlet port 72 into an outlet line 15. The pressure of the fluid in thefluid chamber 60 displaces a diaphragm 25 until the air chamber 45 andfluid chamber 60 are at equilibrium, which is preferably the situationwhen the air and fluid chambers 45 and 60 are at equal pressure.

The pod 10 is primarily made of two parts, a fluid-side shell 30 and anair-side shell 17, that, together, form an enclosure 5 that defines thefluid and air chambers 60 and 45, respectively. The ratio of the minimumto the maximum volume of the air chamber 45, including the volume of theline 40 and port 12, is proportional to the total pressure variationthat can be measured by the transducer attached to the line 40. Thefixed volume defined by the line 40 and port 12 serves as a limit onthis ratio and therefore limits the pressure range that can be measured.Another feature of the pod 10 is that the fluid shell is such that itmust be formed by a mold that has more than two parts, because of theinlet and outlet ports 70 and 72 and the recess that helps define thefluid chamber 60. Since molds with more than two parts are moreexpensive to design and make, this is a disadvantage.

Another feature of the pod 10 is the orientation of the inlet and outletlines 35 and 15 owing to those of the inlet and outlet ports 70 and 72.The orientations require the pod 10 be placed in a straight run oftubing, which can make it difficult to design a compact fluid circuitassembly in which the pod is used. Yet another feature is the use of anintermediate line 40 between the transducer and the pod 10, which makesthe pod assembly larger, requires more parts to be assembled, and hasmore seals which may fail. Another feature of prior art pods in generalis the use of diaphragms that are more permeable than may be desirable.Also, the attachment between the blood side shell 30 and the air sideshell 17 may be made by a compression seal (details not shown) or byanother means of attachment, but in any event, may require additionalsteps to seal the diaphragm within.

SUMMARY

Embodiments include a method of measuring pressure, comprising:positioning on a force measuring station, a pressure pod with adiaphragm and inlet and outlet ports fluidly coupled to a chamber withinthe pressure pod, a first surface of the diaphragm facing the chamber toform a major part of a wall of the chamber, and a second major surfaceof the diaphragm facing away from the chamber and carrying a mechanicalengagement feature. The force measuring station has a mechanicalengagement member configured to engage with the diaphragm mechanicalengagement feature, the mechanical engagement member and the diaphragmmechanical engagement feature being operable to permit the diaphragm toapply a pulling force to the mechanical engagement member, which forceis in a direction tending to move the diaphragm toward the chamber uponapplication of a negative pressure within the chamber. The positioningis effective to permit the mechanical engagement member to access thediaphragm mechanical engagement feature. The method also comprisesapplying a negative pressure to the diaphragm and transmitting a forceresponsive thereto to the mechanical engagement member of the forcemeasuring station; and using the force measuring station, generating asignal responsively to the force applied to the mechanical engagementelement.

Embodiments also include a method of making a pressure measurementdevice, comprising: molding a pod body defining a chamber in a singleshot molding process, the pod body including a chamber and inlet andoutlet ports, the molding including forming an integral diaphragm andthe inlet and outlet ports. The molding can include inserting at leastone projecting mold portion, with a positive draft, which forms at leastone of the inlet and outlet ports and the chamber.

Disclosed embodiments can also include a pressure measuring system,comprising: a pressure pod with a diaphragm and inlet and outlet portsfluidly coupled to a chamber within the pressure pod, a first surface ofthe diaphragm facing the chamber and forming a major part of a wall ofthe chamber and a second major surface of the diaphragm facing away fromthe chamber and carrying a mechanical engagement feature thereon; and aforce measuring station having a mechanical engagement member configuredto engage with the diaphragm mechanical engagement feature, themechanical engagement member and the diaphragm mechanical engagementbeing operable to permit the diaphragm to apply a pulling force to themechanical engagement member, which force is in a direction tending tomove the diaphragm toward the chamber upon application of a negativepressure within the chamber. The force measuring station is configuredto generate a signal responsively to a force applied to the mechanicalengagement element.

Also included in embodiments is a pressure measurement pod for use inblood circuits, comprising: a pressure sensing pod defining a chamber,wherein the pod defines a flexible, moveable, fluid-impermeablediaphragm having a first major side thereof facing the interior of thechamber and a second major side opposite the first major side. Thesecond major side faces outwardly away from the chamber, and thediaphragm has an engagement component configured to engage an externalforce measurement device from the second major side. The pod has portson opposite sides of the chamber on the diaphragm first major side, theinternal surfaces of the chamber and ports being shaped such that anycontour following the surface to the outside of one of the ports tracesonly surfaces characterized by positive or neutral draft angles suchthat invasive mold portions may be withdrawn through the ports therebypermitting the pod body to be molded in a single shot molding process.

Embodiments of the disclosed subject matter further include a pressuremeasurement pod for use in blood circuits, comprising: a pressuresensing pod defining a chamber. The pod defines a flexible, moveable,fluid-impermeable diaphragm having a first major side thereof facing aninterior of the chamber and a second major side opposite the first majorside, the second major side facing outwardly away from the chamber, andthe diaphragm having an engagement component configured to engage anexternal force measurement device from the second major side. The podhas ports on opposite sides of the chamber or the diaphragm first majorside, and the chamber has a major dimension perpendicular to an axis ofone of the ports that is the same or smaller than an internal dimensionof one of the one of the ports.

Also included in embodiments is a pressure measurement system for use inblood circuits, comprising: a pressure sensing pod defining a chamber;and a force measurement device having a base and a force measurementmember to which force is applied to generate a force signal. The poddefines a flexible, moveable, fluid-impermeable diaphragm having a firstmajor side thereof facing an interior of the chamber and a second majorside, opposite the first major side; the second major side facesoutwardly away from the chamber, the diaphragm having an engagementcomponent configured to engage the force measurement member from thesecond major side; the pod having a portion that forms an interferenceengagement with the base; and the force measurement member having amechanical fastening mechanism configured to attach by the interferenceengagement with the diaphragm such that zero force is applied to thediaphragm during attachment to the diaphragm.

According to embodiments, the disclosed subject matter includes apressure measurement device. The device has a housing with a flowchannel, the housing has a single wall forming a self-supportingstructure with a defined flow channel connecting two ports incommunication with the flow channel. The channel has one wall portion ofthe housing that is substantially thinner than a remainder of thehousing. The one wall portion has a major dimension that is no largerthan one of the two ports, thus permitting the housing to be closed by amolding operation and without requiring the attachment of separate partsto close the housing.

The one wall portion may be circular and may constitute a diaphragm. Theone wall portion may be integral with the remainder of the housing andmolded in a single operation from a single quantity of material, such asmedical grade thermoplastic. The one wall portion may be configured suchthat the flow channel housing may be closed with a single moldingoperation and without requiring the attachment of separate parts toclose the housing. an engagement feature may be provided on the one wallportion. The engagement feature may include a protrusion. Alternatively,the engagement feature may include a ferromagnetic element or amechanical fastener feature element. The ports may be located onopposite sides of the channel with axes that are parallel to a majorplane of the one wall portion. A force transducer may be connected tothe one wall portion such that displacement of the one wall portioncauses displacement of the force transducer in directions correspondingto negative as well as positive pressure within the channel. A forcetransducer may be mechanically connected to the one wall portion suchthat displacement of the one wall portion causes displacement of theforce transducer in directions corresponding to negative as well aspositive pressure within the channel. A force transducer may bemagnetically or adhesively connected to the one wall portion such thatdisplacement of the one wall portion causes displacement of the forcetransducer in directions corresponding to negative as well as positivepressure within the channel.

According to embodiments, the disclosed subject matter includes a methodof manufacturing a pressure measuring device. In the method, first andsecond major mold parts are provided which have recesses defining majorparts of a housing. The method includes inserting pins in the first andsecond major mold parts, the pins being shaped to define a flow channelof a molded pressure measuring pod. One of the pins has a major facethat defines an internal surface of a diaphragm. The method furtherincludes closing the first and second major mold parts with the pinstherebetween and injection molding a pressure pod housing and removingthe pressure pod from the mold parts and withdrawing the pins from flowchannel.

In embodiments, the removing may open ports in the housing thatcommunicate through the housing. One of the pins can have a majordimension that is larger than, equal in size to, the diaphragm. One ofthe pins can have a major dimension that is larger than, equal in sizeto, a diameter of the diaphragm. The diaphragm may have an engagementfeature on an outside surface thereof. The engagement feature mayinclude a projection.

According to embodiments, the disclosed subject matter includes apressure measuring device with a flow channel that has a diaphragm in awall thereof, the flow channel forming a self-supporting housing withentry and exit ports providing access to an interior thereof. Thediaphragm has a first engagement element on an external surface thereofand an internal surface facing said channel interior. A force transducerassembly with a second engagement element is configured to connect tothe first engagement element to transmit positive negative displacementof the diaphragm to a force transducer thereof. An engagement mechanismis configured to hold the flow channel at a fixed location relative tothe force transducer.

In embodiments, the force transducer may include a cantilever beam witha strain gauge thereon. The second engagement element may include agripper that actively clamps the first engagement element and the secondengagement element is connected to the force transducer. The flowchannel housing may have a support surface that engages a chassis of theforce transducer assembly and the force transducer assembly has aretention mechanism that holds the flow channel against the supportsurface. The force transducer assembly may have an actuator mechanismthat opens and closes the gripper responsively to commands from acontroller. The force transducer assembly may have an actuator mechanismthat opens and closes the gripper responsively to commands from acontroller. The force transducer assembly may have an actuator mechanismthat opens and closes the gripper responsively to commands from acontroller, the actuator mechanism further including a mechanism thatholds the flow channel housing in place. The force transducer assemblymay have an actuator mechanism that opens and closes the gripperresponsively to commands from a controller, the actuator mechanismfurther including a mechanism that reconfigures to hold the flow channelhousing in place when the gripper is closed and reconfigured to releasethe flow channel housing when the gripper is opened.

According to embodiments, the disclosed subject matter includes apressure measurement pod for use in blood circuits. In the embodiment, apressure sensing pod defines a chamber with a rigid wall portion and anintegral flexible wall portion forming a flexible, moveable,fluid-impermeable diaphragm with a first major side thereof facing theinterior of the chamber and a second major side opposite the first majorside. The second major side faces outwardly away from the chamber, thediaphragm may have a first engagement element. The pod has ports onopposite sides of the chamber or the diaphragm first major side, theinternal surfaces of the chamber and ports being shaped such that anycontour following the surface to the outside of one of the ports tracesonly surfaces characterized by positive or neutral draft angles suchthat invasive mold portions may be withdrawn through the ports therebypermitting the pod body to be molded in a single shot molding process.

The diaphragm may be configured and operative to move only between andto its initial molded position and a position inward from the initialposition, toward the chamber. The diaphragm may be configured andoperative to move outwardly from its as-formed position and inwardlyfrom the as-formed position. A force transducer assembly with a secondengagement element may be configured to connect to the first engagementelement to transmit positive negative displacement of the diaphragm to aforce transducer thereof and an engagement mechanism configured to holdthe pod at a fixed location relative to the force transducer. The forcetransducer may include a cantilever beam with a strain gauge thereon.The second engagement element may include a gripper that actively clampsthe first engagement element and the second engagement element isconnected to the force transducer. The pod housing may have a supportsurface that engages a chassis of the force transducer assembly and theforce transducer assembly may have a retention mechanism that holds thepod against the support surface. The force transducer assembly may havean actuator mechanism that opens and closes the gripper responsively tocommands from a controller. The force transducer assembly may have anactuator mechanism that opens and closes the gripper responsively tocommands from a controller. The force transducer assembly may have anactuator mechanism that opens and closes the gripper responsively tocommands from a controller, the actuator mechanism further including amechanism that holds the pod housing in place. The force transducerassembly may have an actuator mechanism that opens and closes thegripper responsively to commands from a controller, the actuatormechanism further including a mechanism that reconfigures to hold thepod housing in place when the gripper is closed and reconfigured torelease the pod housing when the gripper is opened.

Any of the foregoing devices with a gripper mechanism may employ a knifeedge on the gripper that bites into a protrusion on the diaphragm orflexible wall portion.

According to embodiments, the disclosed subject matter includes a methodof measuring pressure. The method includes securing a flow channel to achassis of a measurement device. The flow channel has a flexible wallwith a protrusion extending from an external surface thereof andclamping the protrusion using a gripper. The method further includesflowing a fluid through the flow channel transmitting forces caused bydisplacement of the flexible wall through the gripper to a forcetransducer. The method further includes generating electrical signalsresponsively to a state of the force transducer and converting theelectrical signals to an indication of pressure.

The securing may include forcing the flow channel to the chassis andpreventing movement of it relative to the chassis. The securing mayinclude activating a drive single drive through a mechanical actuator tocause the clamping and the securing. The mechanical actuator may includea pair of cams. The flowing may include flowing blood. The flowing mayinclude flowing a fluid through a first portion connected to a firstport with a first cross-sectional shape that transitions to a secondportion connected to a second port that may have a secondcross-sectional shape, wherein the first and second cross-sectionalshapes are constant or enlarge toward a respective access of the portsuch that the internal portion of the flow channel may be formed by pinsthat can be withdrawn from the flow channel after molding it. Theflowing may include flowing a fluid through a first portion connected toa first port with a first cross-sectional shape that transitions to asecond portion connected to a second port that may have a secondcross-sectional shape, wherein the first and second cross-sectionalshapes are constant or enlarge toward a respective access of the portsuch that the flow channel may have no more than one internal flow areaexpansion in either flow direction. The flow channel may be aself-supporting rigid pod structure with a fluid channel therethrough.The clamping a protrusion may include forcing a sharp edge into theprotrusion. The clamping a protrusion may include forcing a sharp edgeinto the protrusion using a closing motion that may include no movementalong an axis of the protrusion. The clamping a protrusion may includeforcing a sharp edge into the protrusion using a closing motion that mayinclude no motion that would push the protrusion in any direction.

According to embodiments, the disclosed subject matter includes a methodfor measuring pressure. The method includes securing a flow channel to achassis of a measurement device, the flow channel may have a flexiblewall with a first mechanical engagement feature presented from anexternal surface thereof. The method further includes engaging themechanical engagement feature with a complementary engagement memberconnected to a force transducer and flowing a fluid through the flowchannel. The method includes transmitting forces caused by displacementof the flexible wall through the complementary engagement member to theforce transducer and generating electrical signals responsively to astate of the force transducer and converting the electrical signals toan indication of pressure.

The securing may include forcing the flow channel to the chassis andpreventing movement of it relative to the chassis. The securing mayinclude activating a drive single drive through a mechanical actuator tocause the engaging and the securing. The mechanical actuator may includea pair of cams. The flowing may include flowing blood. The flowing mayinclude flowing a fluid through a first portion connected to a firstport with a first cross-sectional shape that transitions to a secondportion connected to a second port that may have a secondcross-sectional shape, wherein the first and second cross-sectionalshapes are constant or enlarge toward a respective access of the portsuch that the internal portion of the flow channel may be formed by pinsthat can be withdrawn from the flow channel after molding it. Theflowing may include flowing a fluid through a first portion connected toa first port with a first cross-sectional shape that transitions to asecond portion connected to a second port that may have a secondcross-sectional shape, wherein the first and second cross-sectionalshapes are constant or enlarge toward a respective access of the portsuch that the flow channel may have no more than one internal flow areaexpansion in either flow direction. The flow channel may be aself-supporting rigid pod structure with a fluid channel therethrough.The engaging may include clamping the mechanical engagement feature. Themechanical engagement feature may include a protrusion. The engaging mayinclude using a motion that may include no urging of the mechanicalengagement element.

According to embodiments, the disclosed subject matter includes a systemfor measuring pressure in a fluid circuit. A flow channel has a housingwith first and second ports connected by an internal flow path. A forcemeasuring apparatus has an engagement portion to which the flow channelis securely attachable and against which the flow channel isimmobilized. A retention mechanism is configured to hold the flowchannel housing against the engagement portion to maintain a desiredposition thereof relative to the force measuring apparatus. The internalflow path is defined in part by a flexible wall portion that ismechanically engaged with the force measuring member of the forcemeasuring apparatus, the force measuring apparatus is configured togenerate a force indicating signal responsively to displacement of theforce measuring member resulting from displacement of the flexible wallportion. The flexible wall portion is configured to present a smoothinternal surface to the internal flow path. The internal flow pathextends between the access of each port has a hydraulic diameter of nomore than 15 mm at all points therethrough.

The internal flow path may have a cross-section whose aspect ratio doesnot exceed 3. The housing may be a self-supporting inline pod structure.The internal surface of the flow path may have a positive or neutraldraft from any point toward at least one of the first and second portsand at all of said internal surface from said any one point to said atleast one of the first and second ports. The flexible wall portion mayhave a smooth sided protrusion that engages with the force measuringapparatus. The force measuring apparatus may have a gripper mechanismthat grips the protrusion. The protrusion may have a portion with auniform cross-section and the force measuring apparatus grippermechanism has a claw-like end that is configured to close around theprotrusion without any position-selection bias along an axis of theprotrusion such that the claw remains engaged with the protrusion at apoint where it initially contacts the protrusion. The flow channelhousing, including the flexible wall portion and protrusion, may beintegral and of the same material such that they are configured to bemolded as a single element. One of the ports may be larger than theother. The larger of the first and second ports may be connected to afluid circuit for medical treatment and the larger of the ports isconnected to a pump tubing segment and the other is connected to anon-pump tubing segment. The maximum internal dimension at any point ofthe flow path may be limited to as little as 10 mm. The force measuringapparatus may be configured to verify the position or force with whichthe flow channel housing is engaged with the engagement portion. Theinternal flow path may have a cross-section whose aspect ratio does notexceed 3. The flexible wall portion can have a surface facing away fromthe internal flow path which has at all points thereof a positive orneutral draft such that its outer surface can be molded, along with theouter surface of the rest of the housing, by a two part mold. Themaximum dimension of the internal flow path can be limited to varywithin the range of 5 to 10 mm. The housing may have an annular rim andthe force measuring apparatus has a boss configured to mate with theannular rim.

The flexible wall portion may be a diaphragm and the retentionmechanism, housing, and engagement portion may be configured toimmobilize the perimeter of the diaphragm with respect to the forcemeasuring member to minimize displacement of the diaphragm.

According to embodiments, the disclosed subject matter includes a methodfor measuring pressure, comprising: securing a flow channel to a chassisof a measurement device, the flow channel has a flexible wall with afirst mechanical engagement feature presented from an external surfacethereof. The method further includes engaging the mechanical engagementfeature with a complementary engagement member connected to a forcetransducer. The securing is effective to immobilize the flow channelrelative to the force transducer. The method further includes detectingat least one of the position and orientation of the of the flow channelrelative to transducer and comparing to at least one of a predefinedposition and orientation, and generating a signal responsive to thedetecting, and flowing a fluid through the flow channel. The methodincludes transmitting forces caused by displacement of the flexible wallthrough the complementary engagement member to the force transducer andgenerating electrical signals responsively to a state of the forcetransducer and converting the electrical signals to an indication ofpressure.

The securing may include forcing the flow channel to the chassis andpreventing movement of it relative to the chassis. The securing mayinclude activating a drive single drive through a mechanical actuator tocause the engaging and the securing.

The mechanical actuator may include a pair of cams. The flowing mayinclude flowing blood. The flowing may include flowing a fluid through afirst portion connected to a first port with a first cross-sectionalshape that transitions to a second portion connected to a second portthat has a second cross-sectional shape, wherein the first and secondcross-sectional shapes are constant or enlarge toward a respectiveaccess of the port such that the internal portion of the flow channelmay be formed by pins that can be withdrawn from the flow channel aftermolding it. The flowing may include flowing a fluid through a firstportion connected to a first port with a first cross-sectional shapethat transitions to a second portion connected to a second port that hasa second cross-sectional shape, wherein the first and secondcross-sectional shapes are constant or enlarge toward a respectiveaccess of the port such that the flow channel has no more than oneinternal flow area expansion in either flow direction. The flow channelmay be a self-supporting rigid pod structure with a fluid channeltherethrough. The engaging may include clamping the mechanicalengagement feature. The mechanical engagement feature may include aprotrusion. The engaging may include using a motion that may include nourging of the mechanical engagement element.

According to embodiments, the disclosed subject matter includes a methodof measuring pressure, including positioning on a force measuringstation, a pressure pod with a diaphragm and inlet and outlet portsfluidly coupled to a chamber within the pressure pod, a first surface ofthe diaphragm facing the chamber to form a major part of a wall of thechamber, and a second major surface of the diaphragm facing away fromthe chamber and carrying a mechanical engagement feature. The forcemeasuring station has a mechanical engagement member configured toengage with the diaphragm mechanical engagement feature, the mechanicalengagement member and the diaphragm mechanical engagement feature isoperable to permit the diaphragm to apply a pulling force to themechanical engagement member, which force is in a direction tending tomove the diaphragm toward the chamber upon application of a negativepressure within the chamber. The positioning is effective to permit themechanical engagement member to access the diaphragm mechanicalengagement feature. The method includes applying a negative pressure tothe diaphragm and transmitting a force responsive thereto to themechanical engagement member of the force measuring station. The methodincludes using the force measuring station, generating a signalresponsively to the force applied to the mechanical engagement element.The chamber may have a hemicylindrical shape whose wall flows smoothlyinto a full cylindrical shape of one of the inlet and outlet ports. Themethod may include detecting the positioning, and responsively to thedetecting, activating an engagement actuator to bring the mechanicalengagement member into engagement with the diaphragm mechanicalengagement feature. Engagement between the mechanical engagement memberof the force measuring station and the diaphragm mechanical engagementfeature may be by one of an adhesive between the member and the featureand a mechanical coupling.

According to embodiments, the disclosed subject matter includes a methodof making a pressure measurement device including molding a pod bodydefining a chamber in a single shot molding process, the pod body mayinclude a chamber and inlet and outlet ports, the molding may includeforming an integral diaphragm and the inlet and outlet ports. Themolding includes inserting at least one projecting mold portion, with apositive draft, which forms at least one of the inlet and outlet portsand the chamber.

The molding may include inserting two of said projecting mold portionsto form respective inlet and outlet ports and the chamber, the outletport has a greater maximum diameter than the inlet port. The method mayinclude molding a diaphragm to said pod body by way of a projecting moldportion. The projecting mold portions may be pins, each of said pins isof different shapes.

According to embodiments, the disclosed subject matter includes apressure measuring system including a pressure pod with a diaphragm andinlet and outlet ports fluidly coupled to a chamber within the pressurepod, a first surface of the diaphragm facing the chamber and forming amajor part of a wall of the chamber and a second major surface of thediaphragm facing away from the chamber and carrying a mechanicalengagement feature thereon. A force measuring station has a mechanicalengagement member configured to engage with the diaphragm mechanicalengagement feature, the mechanical engagement member and the diaphragmmechanical engagement is operable to permit the diaphragm to apply apulling force to the mechanical engagement member, which force is in adirection tending to move the diaphragm toward the chamber uponapplication of a negative pressure within the chamber. The forcemeasuring station is configured to generate a signal responsively to aforce applied to the mechanical engagement element. The chamber has ahemicylindrical shape whose wall flows smoothly into a full cylindricalshape of one of the inlet and outlet ports.

According to embodiments, the disclosed subject matter includes apressure measurement pod for use in blood circuits with a pressuresensing pod defining a chamber. The pod defines a flexible, moveable,fluid-impermeable diaphragm has a first major side thereof facing theinterior of the chamber and a second major side opposite the first majorside. The second major side faces outwardly away from the chamber, thediaphragm has an engagement component configured to engage an externalforce measurement device from the second major side. The pod has portson opposite sides of the chamber or the diaphragm first major side, theinternal surfaces of the chamber and ports is shaped such that anycontour following the surface to the outside of one of the ports tracesonly surfaces characterized by positive or neutral draft angles suchthat invasive mold portions may be withdrawn through the ports therebypermitting the pod body to be molded in a single shot molding process.The diaphragm may be configured and operative to move only between andto its initial molded position and a position inward from the initialposition, toward the chamber. The diaphragm may be configured andoperative to move outwardly from its as-formed position and inwardlyfrom the as-formed position.

According to embodiments, the disclosed subject matter includes apressure measurement pod for use in blood circuits including a pressuresensing pod defining a chamber. The pod defines a flexible, moveable,fluid-impermeable diaphragm has a first major side thereof facing aninterior of the chamber and a second major side opposite the first majorside. The second major side faces outwardly away from the chamber, thediaphragm has an engagement component configured to engage an externalforce measurement device from the second major side. The pod has portson opposite sides of the chamber or the diaphragm first major side, thechamber has a major dimension perpendicular to an axis of one of theports that is the same or smaller than an internal dimension of one ofthe one of the ports. The chamber may have a cylindrical interiorsurface. The engagement component may include at least one of aprojection integral with the diaphragm, a magnet, a ferromagneticmaterial or member, a Velcro fastener, a hook, an eye, a threadedrecess, a threaded projection, a blade lock, a snap, and a surface withan adhesive face. The engagement component may include a fastener.

Objects and advantages of embodiments of the disclosed subject matterwill become apparent from the following description when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be described in detail below with referenceto the accompanying drawings, wherein like reference numerals representlike elements. The accompanying drawings have not necessarily been drawnto scale. Where applicable, some features may not be illustrated toassist in the description of underlying features.

FIG. 1 shows a cross section of a pressure measuring pod according tothe prior art.

FIG. 2 shows a pressure measurement device according to disclosedembodiments.

FIG. 3 shows a cross section of a fluid circuit portion of a pressuremeasuring device according to a variant of the embodiment of FIG. 2.

FIGS. 4A and 4B show respective views of the embodiment of FIG. 3.

FIGS. 5 and 6 show cross sections of stages in the molding of theembodiment of FIG. 3.

FIG. 7 shows a section of the flow circuit portion of a variant theembodiment of FIG. 2 in relation to a magnet component.

FIG. 8 shows a section of the flow circuit portion of the embodiment ofFIG. 2 in relation to a magnet component.

FIG. 9 shows a flow circuit component incorporating flow circuitportions of the pressure measurement devices according to embodiments asshown and/or described herein.

FIG. 10A shows an exploded section view of a mold assembly forfabricating a pressure pod according to an embodiment of the disclosedsubject matter.

FIG. 10B shows an end view of a pin portion of the mold assembly of FIG.10A according to embodiments of the disclosed subject matter.

FIG. 10C shows the mold assembly of FIG. 10A configured for molding apressure measuring pod during a first molding shot according toembodiments of the disclosed subject matter.

FIG. 10D shows the mold assembly of FIG. 10B modified by a mold portionfor making a diaphragm during a second molding shot according toembodiments of the disclosed subject matter.

FIGS. 10E and 10F shows a pressure pod result of the two-shot moldingprocess in lateral and axial section views according to embodiments ofthe disclosed subject matter.

FIG. 10G shows a pressure pod according to embodiments of the disclosedsubject matter.

FIGS. 11A and 11B show schematic views of a pressure measuring apparatusduring positive and negative pressure measurements, respectively,according to embodiments of the disclosed subject matter.

FIG. 11C shows an alternative mechanism for attaching a forcemeasurement member to a diaphragm according to embodiments of thedisclosed subject matter.

FIG. 12A is a schematic diagram of a pressure pod and force measurementassembly according to embodiments of the disclosed subject matter.

FIG. 12B is a schematic diagram of a pressure pod and force measurementassembly showing a mechanism for placing a jaw-type attachment mechanismin a receptive state according to embodiments of the disclosed subjectmatter.

FIGS. 12C and 12D are schematic diagrams of a force measurement assemblyshowing an alternative mechanism for placing a jaw-type attachmentmechanism in an operational state and a receptive state, respectively,according to embodiments of the disclosed subject matter.

FIGS. 13A and 13B are perspective overhead and bottom views,respectively, of force measurement device according to embodiments ofthe disclosed subject matter.

FIGS. 13C and 13D are views of portions of the force measurement deviceshown in FIGS. 13A and 13B, showing, among other things, a mechanicalengagement member of the force measurement device.

FIG. 14A is another embodiment of a mechanical engagement member portionof a force measurement device according to of the disclosed subjectmatter.

FIGS. 14B and 14C show view of a force measurement device configuredwith the mechanical engagement member portion shown in FIG. 14A.

FIGS. 14D and 14E show different states of the mechanical engagementmember portion shown in FIG. 14A, with FIG. 14D showing an open ordisengaged state of the jaws, and with FIG. 14E showing a closed orengaged state of the jaws.

FIG. 15A shows a pressure pod according to embodiments of the disclosedsubject matter showing features related to single-shot molding andhaving an integral diaphragm.

FIGS. 15B and 15C show mold embodiments which may be used to form thepod of FIG. 15A.

FIG. 16 shows a pressure measurement assembly for using the pod of FIG.15A and other similar devices illustrated herein.

FIG. 17 shows internal details of the assembly of FIG. 16.

FIG. 18A shows the assembly of FIG. 16 in partial cross section.

FIG. 18B shows a feature of an engagement component of a forcetransducer.

FIG. 19 shows a feature that may be used in the embodiment of FIGS. 16through 18.

FIG. 20 shows a feature of a mechanism that may be used in the disclosedembodiments for generating a constant urging force pushing the podagainst a seat of a pressure detection mechanism.

FIG. 21 illustrates an embodiment of a pressure pod in which a straingauge is attached directly to the diaphragm and an electrical connectorconnects leads to and from a driver circuit for reading pressure signalsto form an embodiment that may be included as part of a disposablecircuit.

FIG. 22 shows a machine with a cartridge having multiple pods and aretention fixture attachable thereto.

FIGS. 23A and 23B show alternative arrangements of ports illustratingvariations on the disclosed embodiments.

FIGS. 24A and 24B show an improvement of a pressure pod according to anembodiment of the disclosed subject matter.

FIG. 24C shows an optional diaphragm that may be used with theembodiment of FIGS. 24A and 24B.

FIG. 25 shows a flow chart of various embodiments of a control of apressure measuring system.

DETAILED DESCRIPTION

Referring to FIG. 2, a pressure measurement device 103 has a flow orfluid circuit portion 105 with a first port 106 and a second port 112.In the present embodiment, the first port 106 is larger to accommodate alarger tube in an embodiment where the pressure measurement device 103is to be directly connected to a pump tube portion (see, e.g., FIG. 9).The second port 112 is for connection to a smaller diameter tube. Adiaphragm 122 has a magnet or ferromagnetic material 123 embedded withinit. The diaphragm seals a portion of a continuous lumen spanning between110 and 108 with a cross-sectional area that is substantially uniform toreduce the risk of dead zones that can cause clotting when the device103 is used for measuring blood pressure. Alternatively, the crosssection may vary as a result of the positive draft angles used to allowthe mold pins to be removed so that there is a narrowing from one porttoward the center of the pod and then a widening of the cross section onthe way to the opening of the other port. It is possible for the pins tobe shaped such that the flow area is largest in the middle despite thepositive draft angles, but certain benefits accrue where the areachanges little, including the reduction in turbulence otherwise causedby flow deceleration. Note that flow area inserts may be used to adapttubes to the ports so that the requirements of the beneficial moldingprocess described herein do not have to constrain choices for connectingtubes to the pod. A receptacle 104 receives a mating guide portion 146extending from the body of a blood treatment machine or a chassis of atransducer mechanism 140. The components 104 and 146 cooperate toposition the fluid circuit portion 105 with respect to a magnet 210which in turn is positioned with respect to a load cell 240. Thediaphragm 122 exerts pressure or pulls on the magnet 210, depending onthe pressure in the lumen, which in turn exerts a positive or negativeforce on the load cell 240. A retention device, such as a bar 143 may beemployed to hold the pod 105 against the mating guide portion 146 andmay be provided with a suitable mechanism for engaging and disengaging.Element 104, which forms an annular rim, may seat against the chassis ofthe transducer 140 directly or, as shown, the mating guide portion (orannular boss) may seat against the pod at an interference interfaceindicated at 147 thereby immobilizing the pod housing. With theretention bar 143 or equivalent mechanism, the engagement is suitablefor immobilizing the support of the diaphragm and helping to ensureaccurate measurement with a diaphragm having lower compliance than wouldattend the use of a corrugated diaphragm (See FIG. 24C infra).

FIG. 3 shows the fluid circuit portion 105 according to a differentembodiment in which the diaphragm 122 is formed of a flexible materialthat is magnetic. For example, the diaphragm 122 may be formed of aflexible polymer with embedded ferromagnetic particles. The diaphragm122 may be magnetized or unmagnetized. Also shown in FIG. 3 areinterlocking flutes 114 and 118 that can aid in the creation of adurable seal. Other components of the device of FIG. 3 are labeled withthe same numerals as used in the prior figure so they will not bedescribed again.

FIGS. 4A and 4B show the embodiments of FIG. 2 or 3 from two sides. Asupport rim 142 and a buttress 124 feature are shown. Other componentsof the device of FIGS. 4A and 4B are labeled with the same numerals asused in the prior figures so they will not be described again.

FIGS. 5 and 6 show stages in the manufacture of fluid circuit portion105. In FIG. 5, upper and lower molds 202 and 204 and pins 206, 222, and220 cooperatively define a hollow which when filled with a polymermaterial 208 form the body of the fluid circuit portion 105. As shown inFIG. 6, pin 206 is removed and replaced with a pin 248 which defines aspace which when filled with polymer material 210 forms the diaphragm122. In the latter operation, the polymer forming the body 105 formspart of the mold for the diaphragm and therefore the polymer for thebody may be chosen from materials with a higher melting point than thatused for the diaphragm 122. Alternatively a curable polymer may beemployed. The shapes of the pins may vary from what is shown accordingto the characteristics of the molding process.

FIGS. 7 and 8 show cross sections of the fluid circuit portion 205 witha magnetic diaphragm 212 and a diaphragm 122 with an embedded magneticelement 216, respectively. Other components of the device of FIGS. 7 and8 are labeled with the same numerals as used in the prior figure so theywill not be described again.

FIG. 9 shows a fluid circuit 300 with three pressure pods (fluid circuitportions as is 105) 304, 306, and 308 attached together by a singleframe 310. A pumping portion 302 and arterial blood line 314 and venousblood line 318, and pre- and post-filter lines 312 and 316 to and fromfilter 320, respectively, can be pre-attached so that the components canall be simultaneously positioned and attached to a treatment machine330. This attachment may simultaneously register the pods 304, 306, and308 with transducer fixtures 342 and a peristaltic pump actuator 332.The connections between arterial 314 and venous 318 blood lines areshown figuratively as is a patient 325. An adapter 311 may be providedto allow connection of small diameter tubes as required, in embodimentsin which the pod chamber is the same size as one of the pins used tomold the pod.

FIGS. 10A and 10B show components for fabricating a pressure podaccording to embodiments of the disclosed subject matter. FIGS. 10C and10D show stages in the manufacture of a pressure pod according toembodiments of the disclosed subject matter.

In FIGS. 10A and 10B, pins 406, 408, and 410 and upper and lower molds402 and 404 cooperatively define a hollow, which, when filled with apolymer material, for example, form the body 450 of the pressure pod.Recesses 412, 414, and 416 in upper mold 402 mate with respectiveportions of pin 410, pin 408, and pin 406 (i.e., projecting moldportions), and recesses 418, 420, and 422 in lower mold 404 mate withrespective portions of pin 410, pin 408, and pin 406.

As can be seen from FIGS. 10A and 10B, each of pins 406 and 410 can haveouter end portions that have respective diameters less than maximumdiameters thereof. Further, pin 406 can have a “halved” portion 428 thatbisects the pin 406 horizontally in end view. Thus, one part of pin 406can form a “full” cylinder portion of a flow or fluid circuit portion,and the flow/fluid circuit can transition gradually—such that theflow/fluid channel has a reduced, insignificant amount of dead space orlacks dead space, for example—to a half-cylinder portion formed byportion 428.

FIGS. 10C and 10D show that the pressure pod can be formed in atwo-stage process. As shown in FIG. 10D, pin 408 from FIG. 10C isremoved and replaced with pin 460 that defines a space, which, whenfilled with polymer material forms a diaphragm within a receptacle 462of the pressure pod. FIG. 10D shows that the diaphragm can have amechanical engagement feature 464. As will be discussed in more detaillater, mechanical engagement feature 464 can be engaged by a mechanicalengagement member, such as a gripper, of a pressure sensing or measuringapparatus. The engagement feature 464, when engaged, can be configuredand operative to cause movement of the mechanical engagement memberresponsively to pressure variations due to fluid flow within theflow/fluid channel of the pressure sensing pod. The pod or the deviceused to hold the pod firmly seated for engagement with the forcetransducer device, may employ a spring to generate a consistent urgingforce. The pod of FIG. 100 has a crenelated edge, indicated at 463,which may provide a spring-like effect for this purpose in conjunctionwith a precise hold down latch mechanism, for example, the retention bar824 of FIGS. 16 to 18.

Alternatively, the pressure pod can be formed in a one-stage orsingle-shot process. In such a case, internal surfaces of the chamberand ports of the pressure pod can be shaped such that any contourfollowing the surface to the outside of one of the ports traces onlysurfaces characterized by positive or neutral draft angles such thatinvasive mold portions or projecting portions (e.g., pins 406, 460, and410) may be withdrawn through the ports thereby permitting the pod bodyto be molded in the single shot molding process.

In single-shot or one-stage molding, the diaphragm can be formed inone-piece with the body of the pod 450 so as to have a chamber formed bywall 476 and inlet and outlet ports 472, 474. That is to say, the singlemolding stage can include forming an integral diaphragm with the inletand outlet ports 472, 474, for instance.

Though FIGS. 10A, 10B, 10C, and 10D show three pins per step, three pinsis not a requirement. For instance, each of the pins can be halvedvertically to double the number of pins. Additionally, the pins andrecesses can have different dimensions or geometries (e.g., diameters,oval rather than circular, etc.) than as shown in FIGS. 10A, 10B, and10C. Alternatively, less than three pins may be used, for example, two.

FIGS. 10E and 10F show a pressure pod result of the two-shot moldingprocess in lateral and axial section views, respectively, according toembodiments of the disclosed subject matter. A pressure pod made using asingle-shot process would look similarly, except the diaphragm can beintegral to or formed in one piece with the body of the pod 450. Thus,an interlocking step portion, as shown in FIGS. 10E and 10F for thetwo-shot process may be omitted.

In either case, a pressure pod made via the one-shot or two-shotprocesses can have a fluid chamber with a hemicylindrical shaped wallportion 476 whose wall can flow smoothly into a full cylindrical shapeof the inlet port 472 and/or the outlet port 474. An inner surface 470of the fluid chamber coincides with port 472, which can be a pump tubingport, and can be characterized by positive or neutral draft angles suchthat invasive mold portion 406 may be withdrawn. Wall 468, which caninclude a first major surface of the diaphragm, can form a base or flatportion of the hemicylinder. Such configuration of the pressure podfluid chamber can create an internal volume thereof that reduces anyfluid “dead” spots or space.

An inner wall construction of the pressure pod defining an internalvolume may be constructed differently than shown in FIGS. 10E, 10F, and10G, for example, with differently sized, differently shaped, anddifferent numbers of fluid flow portions. For instance, though FIGS.10E, 10F, and 10G show port 472 having a larger inlet diameter than thatof port 474, the sizes can be different than shown, such as the samesize or reversed in size. Thus, in embodiments, neither of the ports maybe connected to a pump tubing port and can instead be positioned atanother portion of a fluid circuit where the tubing sizes are the same,for instance.

FIG. 100 shows a pressure pod according to embodiments of the disclosedsubject matter, with differently configured inlet and outlet ports 472,474, whereby these ports each have tubing retaining features tofacilitate sealing between and retention of tubing fitted over theports. Other tube retaining features may be employed optionally oralternatively, such as clamps.

Though FIGS. 10E, 10F, and 10G show engagement feature 464 as a nipple-or rod-shaped protrusion, embodiments are not limited to suchconstruction. For instance, engagement feature 464 can be formed as aloop, as a hoop, in a T-shape, in a Y-shape, or as a bulb, for instance.Further, as shown in FIG. 11C, the engagement feature of the diaphragmmay be a recess 526. Of course, like engagement feature 464 mentionedabove, recesses according to embodiments are not limited in shape andgeometry to the configuration shown in FIG. 11C.

Additionally, any embodiments of the diaphragm can have flexibilitypromoting portions, such as groove or grooves 528 shown in FIG. 11C.Optionally, embodiments of the diaphragm can have governor portions,whereby certain flexure of the diaphragm is limited or prevented.Further, the diaphragm itself can be in a form other than what isexplicitly shown in the figures. For instance, diaphragms according toembodiments of the disclosed subject matter can have concave or convexfaces facing inward to the inner volume of the pressure pod.

FIGS. 11A and 11B show schematic views of a pressure measuring apparatus512 during positive and negative pressure measurements, respectively,according to embodiments of the disclosed subject matter.

Pressure measuring apparatus can have a measuring arm 510 supported bytwo points, for instance, and with a strain gauge 508 on an uppersurface thereof. Pressure measuring apparatus 510 can be connected todiaphragm 504 via a disconnectable connection 506, which can be formedby engagement between a mechanical engagement member of the pressuremeasuring apparatus 510 and an engagement feature of the diaphragm 504,such as projection 464 shown in FIGS. 10E through 10F.

Engagement of the diaphragm 504 and the pressure measuring apparatus 510can be provided by at least one of a projection integral with thediaphragm 504 or the pressure measuring apparatus 510, a magnet, aferromagnetic material or member, a mechanical fastener for example, aVelcro fastener, a hook, an eye, a threaded recess, a threadedprojection, a blade lock, a snap, and a surface or surfaces with anadhesive face. For example, FIG. 11C shows an alternative mechanism forattaching a force measurement member of the pressure measuring apparatus510 to a diaphragm, whereby, opposite a second face 524 of the diaphragmis a recess 526 formed on a first face of the diaphragm for locking orremovably locking with a mechanical engagement member in the form of aprojection 526 with an enlarged end portion. The first face of thediaphragm can also include a flexibility promoting groove 528.

Additionally, FIGS. 11A and 11B show schematically the concept of thetransition down in volume from a full cylindrical portion 502corresponding to an inlet or input portion of the pod (e.g., port 472),for example, to a half cylinder portion 520 corresponding to the portionof the flow/fluid channel of the pressure pod associated with the inneror first surface of the diaphragm 504. The diameter of the diaphragm 504may be about the same as a half cylindrical recess, as the inner wall ofthe fluid chamber may be no more than the distance 516 so as to providepositive or neutral draft to all the pins for removal thereof.

FIG. 12A is a schematic diagram of a pressure pod and force measurementassembly according to embodiments of the disclosed subject matter. Somecomponents in FIG. 12A are labeled with the same numerals as used inprior figures so they will not be described again.

Component 540 can represent a machine chassis or support having at anend thereof a mating receiver 533 optionally an extension 515 (dependingupon whether internal or external connection) as well as a guide pattern536. The mating receiver 533 and optional extension 515 can have aconnection member 534 for connecting to a connection member 532 ofdiaphragm 504. Pressure pod body 530 can have a receptacle 538 formating and/or alignment with guide pattern 536. Component 542 can be amechanism that puts connector 534 in a state that allows it to connectwith connection member 532 of diaphragm 504.

For instance, component 542 can cause a member 550 to act on anengagement mechanism 552 such that the engagement mechanism 552 can bepositioned for engaging the connection member 532 of diaphragm 504. FIG.12B is a schematic diagram of a pressure pod 530 and force measurementassembly showing a mechanism 550 for placing a jaw-type attachmentmechanism 552 in a receptive state according to embodiments of thedisclosed subject matter. In order to place attachment mechanism 552 inposition for engagement with connection member 532 of diaphragm 504,mechanism 550 acts on attachment mechanism 552 to place it in an openstate, whereby its “jaws” are opened sufficiently to allow frictionalengagement portions thereof to be moved to an engagement position aroundthe connection member 532. Once in position, in operation, the jaws maybe closed around the connection member 532 to engage and “grasp” theconnection member 532.

FIGS. 12C and 12D are schematic diagrams of a force measurement assemblyshowing an alternative mechanism for placing a jaw-type attachmentmechanism in an operational state and a receptive state, respectively,according to embodiments of the disclosed subject matter. Somecomponents in FIGS. 12C and 12D are labeled with the same numerals asused in prior figures so they will not be described again.

A linear actuator 566 (e.g., a cam actuator) operates to move a movableportion 562 thereof to act on a lever 564 with a fulcrum 565 to moveapart the “jaws” 560 about fulcrum 567 and thereby place the jaw-typeattachment mechanism in a receptive state for placement with respect tothe connection member 532 of the diaphragm. When the linear actuator 566moves its movable portion 562 to the position shown in FIG. 12C, thejaws of the jaw-type attachment mechanism are caused to close around theconnection member 532 of the diaphragm for pressure sensing operation.Optionally, movable portion 562 can be held in position to lock the jawsin a sufficiently tight engaged position with the connection member 532of the diaphragm.

FIGS. 13A and 13B are perspective overhead and bottom views,respectively, of force measurement device 600 according to embodimentsof the disclosed subject matter. FIGS. 13C and 13D are views of portionsof the force measurement device shown in FIGS. 13A and 13B, showing,among other things, a mechanical engagement member of the forcemeasurement device.

Generally speaking, force measurement device 600 can include a base orchassis 602 with an O-ring 603, a linear actuator 604 supported by abridge 606, a sensor portion 608, which can be an optical sensor, and ajaw-type attachment mechanism 610. Force measurement device 600 can alsoinclude a beam 612 with a strain gauge 613 coupled on a top surfacethereof to detect a force associated with pressure-induced movement of adiaphragm operatively coupled to the beam 612 as set forth herein.Pusher 614 is attached to linear actuator 604 and can be caused to acton spreader 615 to open and close the jaws of the jaw-type attachmentmechanism 610. The beam may be supported as a cantilever.

FIG. 14A is another embodiment of a mechanical engagement member portionof a force measurement device 700 according to of the disclosed subjectmatter. In particular, FIG. 14A shows another configuration of jaw-typeattachment mechanism 710 that is operative with a rotary actuator 704.Optionally, an elastic band 711 may be employed to assist with closingand/or engagement of the jaws to a connection member of the diaphragm.Optionally or alternatively, a spring or springs may be used to assistwith closing and/or engagement of the jaws to the connection member ofthe diaphragm.

Of course the jaw-type attachment mechanisms shown herein can be anysuitable configuration. For instance, the jaw-type attachment mechanismscan be a single spring or resilient piece stamped out of a piece ofsteel (e.g., in the form of tongs or tweezers).

FIGS. 14B and 14C show view of a force measurement device 700 configuredwith the mechanical engagement member portion shown in FIG. 14A and alsowith the rotary actuator 704. FIG. 14C additionally shows, in crosssection, force measurement device 700 positioned for operation with apressure pod 750, such as those shown in FIGS. 10E, 10F, and 10G anddescribed herein. Some components in FIGS. 14B, 14C, 14D, and 14E arelabeled with the same numerals as used in prior figures so they will notbe described again.

FIGS. 14D and 14E show different states of the mechanical engagementmember 710 portion shown in FIG. 14A, with FIG. 14D showing an open ordisengaged state of the jaws, and with FIG. 14E showing a closed orengaged state of the jaws, whereby the jaws are engaged and grip orpinch connection member 752 of the diaphragm.

FIG. 15A shows a pressure pod 850 according to embodiments of thedisclosed subject matter. Pressure pod 850 can be formed using asingle-shot molding process in which the diaphragm 868 is formedintegrally with the pressure pod body. A face of the diaphragm facingaway from the fluid channel can have formed integrally with thediaphragm an engagement feature, such as engagement feature 864.Alternatively, that side of the diaphragm 868 can have anotherengagement feature as described herein. Tubing can be connected to fluid(e.g., blood) lines via 872, 874 as shown in FIG. 15A. The ports mayalso provide internal connections, the illustrated type being of thebarb configuration in which tubes surround the outer rim of the port.The arrangement discussed above in which one tub may be larger diameterthan the other to provide for a transition from one type of channel toanother is provided in the present embodiment. For example, port 872 islarger which can accommodate a transition from a pump tubing segment toa smaller tube segment. In many types of tubing sets, a pump tube isused that has precise characteristics to ensure certain expected pumpingperformance which may include repeatability, durability, etc. Suchsegments may be larger diameter or smaller diameter than attached tubingsegments. In such tubing sets, it may be desirable to locate a pressuresensor near the pump tubing segment or on both sides. For example byusing pressure drop across the pump, it may be possible tomathematically calculate a predicted flow rate accurately. By using apressure pod according to the disclosed embodiments in which the portsprovide the additional function of transitioning different types oftubing, for example, different diameter tubing, beneficial cost savingsmay be achieved.

Referring to FIGS. 15B and 15C which represent alternative moldembodiments, the pod 850 of FIG. 15A may be manufactured in a singleshot by inserting respective pins 885 and 886 into ports 872 and 874 ofpod 850 as illustrated in FIGS. 15B and 15C and as discussed with regardto FIG. 10D and elsewhere herein. Then a single mold part 882 may beused to form the upper part and diaphragm 868 as shown in FIG. 15B or apin 881 may be used to form the same portions, which include the annularrim 862. Another mold part 884 is used to form the lower part of thepod.

Another feature of the pod of FIG. 15A is the annular rim 862 which hasa tapered inner surface 863 to guide a location boss on the measurementapparatus. For example, see element 713 which is an annular boss ontowhich the pressure pod 750 is placed. A similar feature is shown at 875in FIG. 18A described further below. The boss may have a complementarytapered surface as shown in the above figures and as indicated in FIG.18A at 876, for example. The annular rim 862 is preferably configured toprovide a solid interference fit against a seat 898 (FIG. 18A) to ensurethere is minimal movement in the Z-direction 821 such that repeatablemeasurements may be obtained. Alternative devices for limiting motion inthe Z-direction are also possible, for example, one or more interlockingdétentes may be provided which encircles the middle portions between thedistal and proximal portions of the annular rim and boss. Anotheralternative is to provide an active mechanism that grips a portion ofthe pod once positioned to limit the movement in the Z-direction. Thesealternatives are not illustrated in the drawings.

FIGS. 16, 17, and 18 show a pressure measurement assembly for using thepod of FIG. 15A and other similar devices illustrated herein. Aretention bar 822 pivots on a hinge 838 to force pod 850 against a seat898. The retention bar 822 is held down by a latch 824 which may haveone interfering edge 823 to hold the latch down and urge it against theseat 898. Alternatively, retention bar 822 may be held in position byfitting into a notch 825 providing retention edges 823 and 891 above andbelow the bar 822 to prevent movement in the Z-direction as illustratedin FIG. 19. Another arrangement may generate a constant force againstthe pod 850 using a resilient member or spring. For example, as shown inFIG. 20, the retention bar 822 may include a leaf spring 827 configuredto urge the pod 850 in the Z-direction with constant force. Instead of aspring the pod may have a spring-like feature. Alternatively, instead ofa leaf spring, a piece of elastomeric material may be used.

Referring to FIGS. 16, 17 and 18, cams 830 and 828 may be driven by amotor 834 to open and close attachment mechanism 842, which has agripper claw 837 that grips the engagement feature 464, 864 of the pod850. Cams 830 and 826 may be provided on a single shaft which may bedriven by a crank element 870 affixed thereto by the motor 834. Themotor may be rotational or linear and in the present embodiment is alinear motor that forces the crank element 870, for instance, to rotatethe cams 830 and 826. Cam 828 rotates to secure the latch 824 whichpivots on a hinge 843. Thus, when a radially maximal portion of the camabuts the lower end of the latch 824, the upper end is held in positionto secure the retention bar 822. Beam 832 has a strain gauge attachedthereto. Beam is connected to attachment mechanism 842 and is flexed bythe change in pressure in the pod 850 as described in previousembodiments. The beam 832 may be supported as a cantilever as in earlierembodiments. The smaller cam 830 rotates to open the attachmentmechanism 832 in a scissor fashion. The cams 828 and 830 are positionedsuch that the latch 824 is secured as the attachment mechanism 842 isclosed around the engagement feature. Standoffs 867 may be provided inthe present and other embodiments to prevent the gripper claw 837 fromclosing too much and cutting the engagement feature. Also, the gripperclaw 837 may have a recess end as indicated at 839 of FIG. 18B tofurther reduce the risk of damaging the engagement feature 864.

A controller 829 may have an input device that allows a user to generatea command signal to open the device 800 to emplace a pod 850. Thecontroller may in turn drive the motor 834 to release the latch and theretention bar which may then be lifted by the user. Simultaneously,according to the description of the cams 828, 830, the attachmentmechanism 842 opens enabling the insertion of the attachment feature864. The pod 850 may then be placed on the boss described above and theretention bar 824 rotated downwardly. Then a command to engage may beentered on the input device and the controller may cause the motor torotate the cams to close the engagement mechanism 842 and engage thelatch 824. Note that in the embodiment of FIGS. 16-18, instead ofmechanical interlock between the engagement mechanism 826 (which isattached to the gripper) and the latch 924, the two mechanisms may beactivated independently by the controller with sensors used to determineif the latch has been closed before the gripper is engaged.

FIG. 21 illustrates an embodiment of a pressure pod assembly 900 inwhich a strain gauge is attached directly to the diaphragm and anelectrical connector 910 connects leads to and from a driver circuit(not shown) for reading pressure signals to form an embodiment that maybe included as part of a disposable circuit. An electrical connector 910has conductors 912 that connect electrically with conductive leads 908of strain gauge 906 attached to a thin flexible metal plate 914 that isdirectly bonded to the diaphragm 916 of pod 920. The leads 904 may beattached to tubing of a tubing set of an embodiment in which theconnector 910 and pod are attached to form a disposable set.Alternatively, the electrical connector may be a separate component 911that is attached to the remainder of the assembly, including the pod920, which forms the disposable set.

FIG. 22 shows a machine with a cartridge having multiple pods and aretention fixture attachable thereto. A machine 941, for example a bloodtreatment machine, peritoneal dialysis cycler, filtration system orother fluid conveying device has an array of pressure sensing stations940 each with an attachment device as in any of the disclosedembodiments, for example, the gripper claw 837. The associated mechanismfor measuring pressure may be housed with other components of themachine 941 in a housing with the alignment boss 938 protruding above asurface of the housing. A fluid circuit cartridge 934 has fluid channelssuch as tubes attached or embedded therein. The fluid circuit haspressure pods 936 which are held onto the bosses 940 by a latching door930 with respective fixtures 932 for engaging the pods 936. Latchmechanisms 943 may be provided to hold the latching door 930. One ormore other actuators or sensors 945 may also be engaged by the latchingdoor. Instead of a latching door or panel other types of hold-downdevices may be used and these may vary in number. Instead of acartridge, other types of fluid circuit structures may be providedincluding ones with no support other than the tubes and circuitcomponents themselves.

FIGS. 23A and 23B show alternative arrangements of ports illustratingvariations on the disclosed embodiments. It should be apparent from thedisclosure that the ports of the pod embodiments do not need to bediametrically opposed and that other arrangements of mating pins canprovide for ports at different angular orientations, for example, asindicated at 960, 962, and 963. A major port 967 whose major dimensioncoincides with that of the diaphragm 966 is provided as in otherembodiments. An engagement feature may also be as discussed in otherembodiments including the alternatives such as a magnet, Velcro., orother attachment.

FIG. 23B shows an embodiment with a port 978 that is aligned with anaxis that forms an angle with respect to the plane of the diaphragm 971.The diaphragm is molded with the aid of a pin whose outline is shown bythe lines 972. The port 978 internal opening is formed with a pin whoseoutline is shown at 974. The resulting ports 976 and 978 may thus form aright angle, for example, with one port being at a right angle to thediaphragm plane.

In the disclosed embodiments, it may be observed that a low volumepressure pod may be configured by employing a direct connection of thediaphragm to a force transducer. Without a compressible fluid betweenthe diaphragm and the force transducer, the compliance that has to beovercome to generate a pressure signal is near zero and so the size andexcursion of the diaphragm can be minimal. Embodiments in which thechamber is formed by a pin whose maximum dimension is that same as thediaphragm diameter are described herein. The small size is enabled bythe direct connection and as a further result the molding process hasbeen simplified, with one embodiment being formed in a single moldingstep with two mold parts. Of course variations of the disclosed moldingoperations and products are possible and also enabled by the disclosure.By having a small diaphragm, the flow channel and in-line chamberbeneath the diaphragm can be formed such that there is very low or nochange in channel diameter or flow area which minimizes turbulence. Thisis particularly desirable in the context of blood flow because it lowersthe risk of thrombogenesis.

It is therefore, apparent that there is provided, in accordance with thepresent disclosure, a device, method, and system which provides forpressure measurement and for making and using the same. Manyalternatives, modifications, and variations are enabled by the presentdisclosure. Features of the disclosed embodiments can be combined,rearranged, omitted, etc. within the scope of the disclosed subjectmatter to produce additional embodiments.

For example, although the pressure pods described generally employ analignment and seating mechanism including an annular boss on themeasurement mechanism and annular rim of the pod, the pair may employother arrangements to achieve the functions described. For example, thepod may be configured with a boss that fits into a recess in themeasurement mechanism. The measurement mechanism term applies to all thedevices described herein that engage with a pod and which include aforce measurement transducer, for example, the structure at 800 in FIG.16 apart from the pod.

Also note that although the embodiments described are principallyprovided with the ability to measure negative pressures as well aspositive, other embodiments employing features of the disclosed subjectmatter may also be based on the present disclosure. For example, insteadof attaching the force sensor to the diaphragm to allow for positive andnegative pressure measurement, the force sensor may merely be heldagainst the diaphragm to allow positive pressures to apply a force. Thussimpler embodiments may be produced. Also note that although thedisclosed pressure pods emphasize the embodiments that are based onsimple molding techniques, more traditional configurations with aninternal chamber that is larger than either of the ports and whichtherefore need to be assembled or require more complicated moldingoperations can still have features of the disclosed embodiments. Forexample, FIGS. 24A and 24B, show a pod 980 that may be formed by weldingtogether molded parts and therefore is capable of having a largerdiaphragm and chamber than the ports 981, 982. The pod 980 may have anengagement element 983 as in above-described embodiments or may have adirectly connected transducer as in the embodiment of FIG. 21.Alternatively such embodiment may have a magnetically coupled connectionbetween a force transducer and the diaphragm.

Referring to FIG. 25, a control procedure for embodiments of thepressure measurement system described herein begins with the transducermechanism in a ready position with an engagement element in a readyposition. For example the clamping mechanism jaws may be in the openposition and any retention features in a released position such that theflow channel device (e.g., pod) can be attached to the transducermechanism. The mechanical positions of the various elements may beverified at S12 and if verified, an output signal indicating read statusmay be generated. This ready signal may be converted to a display outputindicating the readiness of the apparatus to receive a fluid circuit orjust the pressure pod. Then control proceeds to S14. The positions ofthe jaws of the gripper mechanism, for example, may be verified usingangle sensors or optically using an optical encoder or imager. If thetransducer mechanism is not verified as ready, an error signal isgenerated at S28. The error signal may include the output ofinstructions to compensate or fix the problem.

At S14, the attachment of the fluid channel or fluid circuit or pod maybe detected. S14 is optional or could be done after the closure of aretention member at S16. After a retention mechanism, such as theretention member discussed above, is engaged at S16, the proper mountingof the fluid channel is verified at S18. This may include the detectionof the force with which the fluid channel component (e.g. pod) ispressed against the chassis and comparison to a predefined range by thecontroller. In addition, or alternatively, the angle or position of theretention element may be verified optically for example using laserscanner imaging or optical imaging. At S20, if detected configurationmeets a predefined specification, the engagement mechanism (e.g.,gripper mechanism) is actuated and at S22 the completion of theengagement verified by sensors. The same devices as used for in previoussteps may be employed for the S22. In addition, any change in theconfiguration of the flow channel device as a result of the engagementof the actuator (eg. gripper) may be detected and alarmed as necessary.For example, any net displacement of the engagement member may bedetected optically or a force exerted on the gripper mechanism may bedetected that is out of a predefined magnitude range or direction may besensed at S26 and corresponding action taken. Once S26 step is completedand conditions verified to be within bounds, the controller may generatea ready command signal indicating the detected parameters at all pointsof the sequence were within predefined range.

Several terms are used interchangeable, and some are hypernyms of othersused in the present specification. For example, engagement mechanism ormember is generic to gripper which is generic to claw, but it should beclear that these are abstractions of the detailed embodiments thatinclude 560, 610, and the like, though the more generic terms areintended to encompass more embodiments than the more specific terms.Similarly, the term flow channel is generic to pod. The features of thedisclosed subject matter may be applied to flow channels that areincorporated in a fluid circuits with many elements and may beintegrated in number in such configurations. The pod configuration isnot essential to the provision of all the features described, so forexample, a cartridge structure may have a flow channel therein and a lowcompliance diaphragm forming a wall of the channel which may takeadvantage of the teachings of presently disclosed subject matter.

Among the features described above which may be noted are the following.

-   -   1. A mechanism is provided for immobilizing the diaphragm        support. This feature is useful where, as here, the diaphragm is        flat and therefore will experience a restoring force with only a        very minimal displacement. Alternative embodiments such as shown        in FIGS. 24A and 24B can have a corrugated diaphragm as shown in        FIG. 24C in which case, the support of the diaphragm support can        be more compliant. The immobilization is provided in        embodiments, for example, by the rigid pod housing supporting        the diaphragm perimeter, the annular rim (e.g., 862) and the        seat on the chassis of the transducer mechanism (e.g., 898).    -   2. The retention element or protrusion may be configured to        present no position bias that would create a force upon        engagement by the gripper mechanism. For example, the sides of        the protrusion embodiments shown are smooth featureless allowing        the edges of the gripper to engage it where the edges of the        gripper initially make contact with the engagement member.        Contrast this with a member having a recess, which could bias        the diaphragm upon being engaged by a mating gripper mechanism.    -   3. The gripper has a pivot access that is remote from the        engagement member so that the rotation after initial engagement        produces minimal axial movement of the diaphragm as a result of        the pivoting of the jaws after the initial contact with the        engagement member.    -   4. The rigid housing of a pod provides additional support to the        diaphragm thereby further ensuring the diaphragm support is        immobile with respect to the transducer mechanism chassis. Note        it is assume the chassis is the base that supports the strain        gauge element so that the movement of the diaphragm relative to        the chassis translates to pressure indications.    -   5. A centering mechanism, such as the combination of an annular        rim on the pod housing and the boss on the transducer chassis        with associated tapered surfaces, ensures the engagement member        is positioned in the transducer mechanism.    -   6. The immobilization features and direct connection between the        diaphragm and transducer make it possible to use a low        compliance diaphragm. This further enables the molding        techniques described above. It also enables a small size        diaphragm which provide benefits of allowing a small diameter        flow channel and thereby the reduction of flow decelerations        that attend the use of a conventional pod. The ability to use a        diaphragm of low compliance is also associated with the use of a        low aspect ratio channel. In the disclosed embodiments, the        aspect ratio is below 3 and in some embodiments, below 4.    -   7. The low aspect ratio in combination with small flow area        provides a high velocity, low strain rate fluid dynamics which        are highly friendly to blood flow. This is combined with a flow        area transitions of low magnitude which correspond to low        acceleration/deceleration and concomitant low turbulence. For        example, the pod embodiments may have a diaphragm diameter        between 5 and 10 mm, a first port diameter between 5 and 10 mm        and a second port diameter between 3 and 8 mm. in an exemplary        embodiment, the first port is 8 mm, the diaphragm is 8 mm, the        second port is 5 mm which corresponds to hydraulic diameter of        the first port being about 8 mm, the internal channel below the        diaphragm about 5 mm and the second port, 5 mm. The maximum        aspect ratio of the latter embodiment is 2. The path through the        embodiments is minimally-tortuous as well. Thus the variation in        hydraulic diameter, it will be seen, can be only 60% while still        providing for positive or neutral draft shape that allows the        single-shot molding to be used for fabrication. Note the        calculations assume the shape of the pod embodiment illustrated        at 850 in the drawings with cross section as discussed with        reference to FIGS. 12A and 12B.    -   8. The flat internal surface of the diaphragm provides a neutral        draft for removal of a molding pin, but it also has benefits in        terms of blood flow in that it presents a smooth surface to the        flow which also minimizes turbulence.

In embodiments, the aspect ratio of the flow channel of the pressure podis less than three. In embodiments, the maximum dimension of the channelfrom port to port is 20 mm. In further embodiments, the maximumdimension is 15 mm. In still further embodiments, the maximum dimensionis 10 mm. In embodiments the maximum dimension is 8 mm. In embodiments,the maximum aspect ratio from port to port is 2. In a particularembodiment the maximum dimension of 10 mm from port to port is combinedwith the maximum aspect ratio of 2. In any of the embodiments, thehydraulic diameter varies by no more than 100% and in furtherembodiments, the hydraulic diameter varies by no more than 80% and instill further embodiments by no more than 60%. The hydraulic diameterfrom port to port, in embodiments, may range from 5 to 15 mm. Inembodiments, the hydraulic diameter remains at all points along the flowpath, in a range between 4 mm and 10 mm. In embodiments, the hydraulicdiameter remains at all points along the flow path, in a range between 5mm and 8 mm.

All of the pod configurations may be modified to have any of a varietyof shapes and the pod shape is not necessarily essential to providing atleast some of the features described herein. Generally, a variety ofself-supporting flow channels can be configured in any of a variety ofshapes, with a diaphragm in a wall of the channel, and configured toprovide the low internal volume, negative pressure-measuringcapabilities of the embodiments described herein. Such flow channelscould be formed as part of a larger network structure that has otherflow elements such as valves, sensors, and/or pumping sections, forexample.

Various mechanisms for immobilizing the housing of the pressure pod canbe used. In addition to the détente and retention bar approaches, thepod may be secure by a retention clamp which engages a flange at themouth of the annular rim, vacuum suction, by a magnetic force, or by anyof a variety of mechanisms.

It will be appreciated that the modules, processes, systems, andsections described above can be implemented in hardware, hardwareprogrammed by software, software instruction stored on a non-transitorycomputer readable medium or a combination of the above. For example, amethod for generating a pressure signal can be implemented, for example,using a processor configured to execute a sequence of programmedinstructions stored on a non-transitory computer readable medium. Forexample, the processor can include, but not be limited to, a personalcomputer or workstation or other such computing system that includes aprocessor, microprocessor, microcontroller device, or is comprised ofcontrol logic including integrated circuits such as, for example, anApplication Specific Integrated Circuit (ASIC). The instructions can becompiled from source code instructions provided in accordance with aprogramming language such as Java, C++, C#.net or the like. Theinstructions can also comprise code and data objects provided inaccordance with, for example, the Visual Basic™ language, LabVIEW, oranother structured or object-oriented programming language. The sequenceof programmed instructions and data associated therewith can be storedin a non-transitory computer-readable medium such as a computer memoryor storage device which may be any suitable memory apparatus, such as,but not limited to read-only memory (ROM), programmable read-only memory(PROM), electrically erasable programmable read-only memory (EEPROM),random-access memory (RAM), flash memory, disk drive and the like.

Furthermore, the modules, processes, systems, and sections can beimplemented as a single processor or as a distributed processor.Further, it should be appreciated that the steps mentioned above may beperformed on a single or distributed processor (single and/ormulti-core). Also, the processes, modules, and sub-modules described inthe various figures of and for embodiments above may be distributedacross multiple computers or systems or may be co-located in a singleprocessor or system. Exemplary structural embodiment alternativessuitable for implementing the modules, sections, systems, means, orprocesses described herein are provided below.

The modules, processors or systems described above can be implemented asa programmed general purpose computer, an electronic device programmedwith microcode, a hard-wired analog logic circuit, software stored on acomputer-readable medium or signal, an optical computing device, anetworked system of electronic and/or optical devices, a special purposecomputing device, an integrated circuit device, a semiconductor chip,and a software module or object stored on a computer-readable medium orsignal, for example.

Embodiments of the method and system (or their sub-components ormodules), may be implemented on a general-purpose computer, aspecial-purpose computer, a programmed microprocessor or microcontrollerand peripheral integrated circuit element, an ASIC or other integratedcircuit, a digital signal processor, a hardwired electronic or logiccircuit such as a discrete element circuit, a programmed logic circuitsuch as a programmable logic device (PLD), programmable logic array(PLA), field-programmable gate array (FPGA), programmable array logic(PAL) device, or the like. In general, any process capable ofimplementing the functions or steps described herein can be used toimplement embodiments of the method, system, or a computer programproduct (software program stored on a non-transitory computer readablemedium).

Furthermore, embodiments of the disclosed method, system, and computerprogram product may be readily implemented, fully or partially, insoftware using, for example, object or object-oriented softwaredevelopment environments that provide portable source code that can beused on a variety of computer platforms. Alternatively, embodiments ofthe disclosed method, system, and computer program product can beimplemented partially or fully in hardware using, for example, standardlogic circuits or a very-large-scale integration (VLSI) design. Otherhardware or software can be used to implement embodiments depending onthe speed and/or efficiency requirements of the systems, the particularfunction, and/or particular software or hardware system, microprocessor,or microcomputer being utilized. Embodiments of the method, system, andcomputer program product can be implemented in hardware and/or softwareusing any known or later developed systems or structures, devices and/orsoftware by those of ordinary skill in the applicable art from thefunction description provided herein and with knowledge of medicaldevices and/or computer programming arts.

Moreover, embodiments of the disclosed method, system, and computerprogram product can be implemented in software executed on a programmedgeneral purpose computer, a special purpose computer, a microprocessor,or the like.

It is, thus, apparent that there is provided, in accordance with thepresent disclosure, pressure measurement devices methods and systemsincluding control system which may include programmable processors andrelated effecters. Many alternatives, modifications, and variations areenabled by the present disclosure. Features of the disclosed embodimentscan be combined, rearranged, omitted, etc., within the scope of theinvention to produce additional embodiments. Furthermore, certainfeatures may sometimes be used to advantage without a corresponding useof other features. Accordingly, Applicants intend to embrace all suchalternatives, modifications, equivalents, and variations that are withinthe spirit and scope of the present invention.

Furthermore, certain features of the disclosed embodiments may sometimesbe used to advantage without a corresponding use of other features.Accordingly, Applicants intend to embrace all such alternatives,modifications, equivalents, and variations that are within the spiritand scope of the present disclosure.

What is claimed is:
 1. A system for measuring pressure in a fluidcircuit, comprising: a disposable fluid circuit portion with first andsecond ports connected by an internal flow path; a force measuringapparatus with a force measuring member and an engagement portion, fluidcircuit portion being securely attachable to said engagement portion toimmobilize said fluid circuit portion relative to the force measuringapparatus; force applied to the force measuring member causing a forceindication output signal of the force measuring apparatus; a retentionmechanism that releasably holds, to permit replacement thereof, thefluid circuit portion against the engagement portion by urging itthereagainst to maintain a desired position of the fluid circuit portionrelative to the force measuring apparatus; the internal flow path beingdefined in part by a flexible wall portion that is directly connected tothe force measuring member of the force measuring apparatus, the forcemeasuring apparatus being configured to generate a force-indicatingsignal responsively to displacement of the force measuring memberresulting from displacement of the flexible wall portion; the flexiblewall portion being round and flat, the flexible wall portion and theengagement portion being operable to permit the flexible wall portion toapply forces in opposing directions effective to indicate positive andnegative pressures in the internal flow path; wherein the flexible wallportion is of uniform thickness, and shaped to present a smooth internalsurface to the internal flow path; the internal flow path extendingbetween the access of each port having a hydraulic diameter of no morethan 15 mm at all points therethrough wherein the fluid circuit portion,including the flexible wall portion, are integral and of the samematerial such that they are configured to be molded as a single element.2. The system of claim 1, wherein the internal flow path has across-section whose aspect ratio does not exceed
 3. 3. The system ofclaim 1, wherein: the fluid circuit portion is a self-supporting inlinepod structure; and the flexible wall portion is round with a diameterequal to an internal diameter of one of said first and second ports;wherein the internal surface of the flow path has a positive or neutraldraft from any point toward at least one of the first and second portsand at all of said internal surface from said any one point to said atleast one of the first and second ports.
 4. The system of claim 1,wherein the internal surface of the flow path has a positive or neutraldraft from any point, toward at least one of the first and second portsand at all of said internal surface from said any one point to said atleast one of the first and second ports.
 5. The system of claim 1,wherein the flexible wall portion has a smooth sided protrusion thatengages ,with the force measuring apparatus.
 6. The system of claim 5,wherein the force measuring apparatus has a gripper mechanism that gripsthe protrusion.
 7. The system of claim 6, wherein the protrusion has aportion with a uniform cross-section and the force measuring apparatusgripper mechanism has a claw-like end that is configured to close aroundthe protrusion without any position-selection bias along an axis of theprotrusion such that the claw remains engaged with the protrusion at apoint where it initially contacts the protrusion.
 8. The system of claim1, wherein one of the ports is larger than the other, and the larger ofthe first and second ports are connected to a fluid circuit for medicaltreatment and the larger of the ports is connected to a pump tubingsegment and the other is connected to a non-pump tubing segment.
 9. Thesystem of claim 1, wherein the force measuring apparatus is configuredto verify the position or force with which the fluid circuit portion isengaged with the engagement portion.
 10. The system of claim 1, whereinthe flexible wall portion has a surface facing away from the internalflow path which has at all points thereof a positive or neutral draftsuch that its outer surface can be molded, along with the outer surfaceof the rest of the fluid circuit portion, by a two part mold.
 11. Thesystem of claim 1, wherein the fluid circuit portion has an annular rimand the force measuring apparatus has a boss configured to mate with theannular rim.
 12. The system of claim 1, wherein the flexible wallportion is a diaphragm and the retention mechanism, fluid circuitportion, and engagement portion are configured to immobilize theperimeter of the diaphragm with respect to the force measuring member tominimize displacement of the diaphragm.
 13. A pressure measuring device,comprising: a pressure pod configured for in-line flow and having firstand second ports opening to a fluid chamber; the fluid chamber having adiaphragm forming a wall portion thereof; the fluid chamber with across-section whose aspect ratio is less than 3 and has a maximumdimension in cross-section that is no more than 15 mm, wherein thediaphragm has a flat and smooth internal surface; a force transducerdirectly mechanically coupled to the diaphragm and configured togenerate pressure-indicating signals responsively to displacement of thediaphragm; wherein every internal portion of the interior surface of thepressure pod has a positive or neutral draft to one of the ports and allportions leading from such internal portion to said one of the ports hasa positive or neutral draft out to that one of the ports; wherein theinternal surface of the pod is such that the pod can be molded using twopins in a single action molding process.
 14. The device of claim 13,wherein the flow channel from port to port has a hydraulic diameter thatvaries by not more than 80%.
 15. The device of claim 13, wherein in theflow channel defined by the pod, the hydraulic diameter remains at allpoints along the flow path, in a range between 4 mm and 10 mm.
 16. Amethod for measuring pressure, comprising: flowing a fluid through aflow channel having a hydraulic diameter of less than 10 mm and a crosssectional aspect ratio that does not exceed 2; wherein the channel has aflexible wall portion, transmitting forces caused by displacement of theflexible wall portion to a force transducer; generating electricalsignals responsively to a state of the force transducer and convertingthe electrical signals to an indication of pressure.
 17. The method ofclaim 16, wherein the flowing includes flowing blood.